They found that in addition to testicular germ cell tumors, there was a decrease in piRNA expression and DNA hypomethylation of LINE1 (PIWI/piRNA target sequence) in primary seminoma and non-seminoma testicular tumors, and their reduction also led to epigenetic inactivation of PIWI-like protein (PIWIL1, PIWIL2, and PIWIL4) and their related TDRD1 protein gene in human testicular tumorigenesis. The gene discussed is PIWIL1; the disease is seminoma.